Curable resin composition, coating composition, coating method and coated article

ABSTRACT

A curable resin composition insuring good curability and having an excellent high-solid feature, a sufficient storage stability comprising 5 to 80 weight % of a polymer containing free and esterified carboxyl groups and having an acid value of 50 to 300 (mgKOH/g)(1e), 1 to 80 weight % of a polymer containing hydroxyl and epoxy groups and having an epoxy equivalent of 200 to 1000 and a hydroxyl equivalent of 250 to 1500 (2d), and 1 to 50 weight % of an alkoxyl group-containing silicone polymer having an alkoxyl equivalent of 50 to 1500 (3a), 0.1 to 5.0 weight % of a quaternary ammonium salt catalyst (4a) and 0.1 to 5.0 weight % of a monoalkyltin compound (5a).

FIELD OF THE INVENTION

The present invention relates to a curable resin composition capable offorming a coating film of excellent quality in terms of acid resistance,mar resistance and appearance and, therefore, finding application in thefields of automotive top coatings, coil coatings, household electricalappliances, plastics and electrical materials, among other uses, and toa coating composition, a method of forming a coating film, and a coatedarticle each as obtainable or implementable using said curable resincomposition.

PRIOR ART

Automotive top coatings and a variety of coatings dedicated to the samepurpose are required to possess a function to provide an aestheticappearance and prolong the life of the car by evading damages due towinds and rains, stones, muds and dust by constituting the outermostlayer of the coating structure inclusive of the primer and intermediatecoating layers on the body of a car or the like and, therefore, mustprovide a film with high mar resistance and good appearance. The resincompositions used in such coatings are so designed that they will showviscosities before coating within a certain range that facilitatescoating and, after application, may be easily cured to provide necessaryresistance and appearance, that is to say they may exhibit a longstorage stability and the optimum curability.

The conventional curing system for such automotive top coatings is anaminoplast curing agent such as a melamine resin which reacts with thehydroxyl groups of a hydroxyl group-containing polymer to achievecuring. However, the above curing system is unsatisfactory in acidresistance and the coating film obtained is liable to develop defectsowing to acidic rains which have recently been a major problem. Thedefects are generally attributed to the triazine nucleus of the melamineresin and no improvement in acid resistance could be realized unless theuse of melamine resin was avoided or restricted to a sufficiently lowlevel to avoid said defects.

As a curing system not using a melamine resin, a method employing apolyisocyanate compound is known but the toxicity problem associatedwith the isocyanate has not been resolved. Therefore, a curable resincomposition of high nonvolatile content comprising a polyoxide of lowmolecular weight, a hydroxyl group-containing polyfunctional substanceof low molecular weight, a curing agent essentially comprising ananhydride, and an acid catalyst was proposed (Japanese Kokai PublicationSho-63-84674). However, this composition was found to have thedisadvantage that because its ingredients are so reactive to each otherthat it cannot be stored in one package, presenting a storage stabilityproblem.

In view of the above state of the art, a technology employing both (1) ahalf-esterified copolymer and (2) an epoxy group- and hydroxylgroup-containing compound in a defined ratio to overcome theabove-mentioned disadvantage was disclosed (Japanese Patent ApplicationHei-2-91299). This composition provided high acid resistance to overcomethe above disadvantage but was inadequate in mar resistance.

In view of the above problem, a technology was proposed in which, inaddition to the use of both (1) a half-esterified (inclusive ofhalf-thioesterified and half-amidated) copolymer and (2) an epoxy group-and hydroxyl group-containing compound, (3) at least one member selectedfrom among an acrylic polymer, a fluorine-containing copolymer and apolyester resin, and (4) a melamine resin are used to provide acomposition according to a well-considered formula to thereby overcomethe above-mentioned disadvantage (Japanese Kokai PublicationHei-4-363374). Although it contains a melamine resin, this compositionsatisfies the acid resistance requirement to a certain extent andprovides good mar resistance.

In the above technologies, the curing systems used essentially requiresufficiently high functional group concentrations, so that theinevitable high viscosities called for fair amounts of solvents. Assuch, these technologies are unsuitable for production in areas whereregulations for environmental protection such as control over VOC(volatile organic compounds) are in force and, moreover, are deterrentsto control of atmospheric pollution. Therefore, even in the field ofhigh-solid compositions, a demand was felt for provision of acomposition improved in the above aspect.

Under the circumstances, as the result of research into a high-solidresin composition satisfying the above performance requirements, atechnology was disclosed in which, in addition to the use of both (1) ahalf-esterified copolymer and (2) an epoxy group- and hydroxylgroup-containing compound, (3) a hydroxyl group- and carboxylgroup-containing silicone polymer is used to constitute a compositionaccording to a defined formula to thereby overcome the abovedisadvantages (Japanese Patent Application Hei-5-224239).

The above technology adopts an acid anhydride curing system and meetsboth the acid resistance and high-solid requirements but does notsatisfy more sophisticated appearance and mar resistance requirements.Then, it was discovered that the above disadvantages can be obviated bya technology such that, in addition to the use of (1) a half-esterifiedcopolymer, (2) an epoxy group- and hydroxyl group-containing polymer and(3) a hydroxyl group- and carboxyl group-containing silicone polymer,(4) at least one pigment-dispersing resin selected from among alkydresin, polyester resin, and basic substance-modified products of them,(5) a pigment, and (6) an aminoplast curing agent (melamine resin) areused to constitute a composition according to a defined formulation andaccordingly a Letters Patent was applied for (Japanese PatentApplication Hei-5-303849).

It will be obvious from the process of development of the abovetechnologies that in the effort to improve resin compositions forcoatings such as automotive top coatings, addition of an aminoplastcuring agent was first contemplated in an attempt to insure a sufficientstorage stability and optimal curability and a subsequent endeavor tofind a new curing system over coming the drawback of consequentlyreduced acid resistance resulted in a resin composition comprising botha half-esterified copolymer and an epoxy group- and hydroxylgroup-containing polymer and not containing an aminoplast curing agent,which was followed, in the course of research for developing ahigh-solid coating, by the idea of employing a silicone polymer havingboth hydroxyl and carboxyl groups.

However, because the silicone polymer used in the above technology is asilicone polymer provided with both carboxyl and hydroxyl functionsthrough reaction of the hydroxyl group of a silicone polymer with anacid anhydride group, it has the disadvantage of poor curability due toan insufficient number of functional groups, with the result that whenit is used in a coating composition, the glass transition temperature(Tg) cannot be increased. This disadvantage can be overcome byincorporating a limited amount of an aminoplast curing agent forimproved curability but this practice inevitably entails a certaindecrease in the acid resistance which is necessary for withstanding theinfluence of acidic rains.

Incidentally, when a silicone polymer has alkoxyl groups, a storagestability becomes deteriorated and it is desired to solve this problem.

In view of the above state of the art, the present invention has for itsobject to provide quite a new curable resin composition which exhibitsgood curability essentially without the aid of an aminoplast curingagent, has a fully high-solid characteristic and, in addition, has asufficent storage stability.

SUMMARY OF THE INVENTION

The gist of the present invention resides in the technology that acurable resin composition is provided by using

5 to 80 weight % of a polymer containing free and esterified carboxylgroups and having an acid value of 50 to 300 (mg KOH/g) (1e) asobtainable by reacting an acid anhydride group-containing polymer (1c),which is obtainable by copolymerizing 10 to 40 weight % of an acidanhydride group-containing ethylenically unsaturated monomer (1a) with90 to 60 weight % of a copolymerizable other ethylenically unsaturatedmonomer (1b), with a monohydric alcohol of 1 to 12 carbon atoms (1d) inthe ratio (the number of mols of acid anhydride group in acidanhydride-containing polymer (1c)/(the number of mols of hydroxyl groupin monohydric alcohol (1d) of 1/10 to 1/1,

1 to 80 weight % of a hydroxyl group- and epoxy group-containing polymerhaving an epoxy equivalent of 200 to 1000 and a hydroxyl equivalent of250 to 1500 (2d) as obtainable by copolymerizing 5 to 60 weight % of ahydroxylalkyl (meth)acrylate monomer (2a) of the general formula (I):##STR1## (wherein R represents hydrogen or methyl; A represents astraight-chain or branched alkylene group of 2 to 8 carbon atoms; yrepresents a whole number of 3 to 7; z represents a whole number of 0 to4) with 10 to 60 weight % of an epoxy group-containing ethylenicallyunsaturated monomer (2b) and 0 to 85 weight % of an ethylenicallyunsaturated monomer (2c) copolymerizable therewith,

1 to 50 weight % of an alkoxyl group-containing silicone polymer havingan alkoxyl equivalent of 50 to 1500 (3a) of the general formula (II):##STR2## (wherein R¹, R², R³, R⁴, R⁵, and R⁶ are the same or differentand each represents alkyl of 1 to 10 carbon atoms, phenyl, phenethyl,alkoxyl of 1 to 5 carbon atoms, R⁷ --Si(OR')₃, R⁷ --Si(OR')₂ CH₃, R⁷--Si(OR')(CH₃)₃, or R⁷ --Y; R⁷ represents a straight-chain or branchedalkylene group which may have an ether bond and/or an ester bond; R"represents alkyl of 1 to 5 carbon atoms; Y represents an epoxygroup-containing acyclic or cyclic hydrocarbon residue; g represents awhole number of 1 to 20, m represents a whole number of 0 to 4, nrepresents a whole number of 0 to 2; the order of the parenthesizedgroups occurring in g, m and n repetitions is random and not restrictedto the formula shown),

0.1 to 5.0 weight % of a quaternary ammonium salt catalyst (4a), and

0.1 to 5.0 weight % of a monoalkyltin compound (5a). The compoundingpercentages of (1e), (2d), (3a), (4a) and (5a) are based on thenonvolatile matter in the above composition, and the proportions of themonomers for said components (1e) and (2d) are based on the total amountof monomers constituting each components.

The present invention is further concerned with a coating compositioncontaining said curable resin composition, a method of forming a coatingfilm using said coating composition, and a coated article as obtainedusing said coating composition.

DETAILED DESCRIPTION OF THE INVENTION

The first component constituting the curable resin composition of thepresent invention is a polymer (1e) containing both free and esterifiedcarboxyl groups and having an acid value of 50 to 300 (mgKOH/g). Thispolymer (1e) can be prepared by reacting an acid anhydridegroup-containing polymer (1c) with a monohydric alcohol (1d) of 1 to 12carbon atoms for half-esterification.

The acid anhydride group-containing polymer (1c) mentioned above can beprepared by copolymerizing 10 to 40 weight %, preferably 15 to 30 weight%, of an acid anhydride group-containing ethylenically unsaturatedmonomer (1a) with 60 to 90 weight %, preferably 70 to 85 weight %, of acopolymerizable other ethylenically unsaturated monomer (1b).

When the proportion of said acid anhydride group-containingethylenically unsaturated monomer (1a) is less than 10 weight %, nosufficient curability can be obtained, while the use of an excess over40 weight % results in an excessively hard, brittle coat with inadequateweather resistance.

The acid anhydride group-containing ethylenically unsaturated monomer(1a) mentioned above is not particularly limited in kind only if it isan ethylenically unsaturated monomer containing a carboxylic anhydridegroup and includes itaconic anhydride, maleic anhydride and citraconicanhydride, among others.

The other ethylenically unsaturated monomer (1b) copolymerizable withsaid acid anhydride group-containing ethylenically unsaturated monomer(1a) is not particularly limited in kind, either, only if it does notadversely affect the acid anhydride group. Thus, monomers of 2 to 15carbon atoms containing one ethylenically unsaturated bond are preferredand those of 3 to 12 carbon atoms are still more preferred. Moreover,the use of two or more different monomers particularly contributes toenhanced compatibility of resins.

The free carboxyl groups of the polymer (1e) containing both free andesterified carboxyl groups can be derived from the use of a carboxylgroup-containing monomer (1b²) as said copolymerizable otherethylenically unsaturated monomer (1b) for copolymerization with said(1a), followed by reaction of the resulting polymer (1c) with themonohydric alcohol (1d) as will be described hereinafter. In this case,said carboxyl group-containing monomer (1b²) is used only in an amountproviding for an acid value within the range of 50 to 300 (mgKOH/g) for(1e). The kind of said carboxyl group-containing monomer (1b²) is notparticularly limited. Thus, acrylic acid and methacrylic acid, amongothers, can be used and one or more of them can be used in combination.

The copolymerizable other ethylenically unsaturated monomer (1b)mentioned above further includes, in addition to said monomer (1b²),such other monomers as styrene and its derivatives, e.g.α-methylstyrene, para-t-butylstyrene, etc.; (meth)acrylic esters such asmethyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate,n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate,2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl(meth)acrylate, isobornyl (meth)acrylate, etc.; and VeoVa-9, VeoVa-10,etc. (manufactured by Shell). When styrene or a styrene derivative isused for said copolymerizable other ethylenically unsaturated monomer(1b), it is used preferably within the range of 0 to 40 weight %. If thelimit of 40 weight % is exceeded, weather resistance is adverselyaffected.

The copolymerization reaction between said acid anhydridegroup-containing ethylenically unsaturated monomer (1a) and saidcopolymerizable other monomer (1b) can be carried out in the knownmanner, for example by a radical polymerization method in solution,either at atmospheric pressure or at elevated pressure and apolymerization temperature of 100° to 200° C. for a polymerization timeof 3 to 8 hours. As the polymerization initiator, an azo type initiatoror a peroxide type initiator can be advantageously employed and itspreferred amount is 0.5 to 15 parts by weight relative to 100 parts byweight of the total monomer. To the above monomer composition, otheradditives such as a chain transfer agent can be added.

The preferred number average molecular weight of the acid anhydridegroup-containing polymer (1c) obtained by the above copolymerizationreaction is 1500 to 8000. If the number average molecular weight is lessthan 1500, the curability of the curable resin composition will beinadequate. If it exceeds 8000, the polymer viscosity is increased tointerfere with the manufacture of a high-solid coating composition. Themore preferred molecular weight range is 1800 to 4000. These molecularweight values can be determined by, for example, gel permeationchromatography (GPC).

The above-mentioned acid anhydride group-containing polymer (1c)preferably contains at least 2 acid anhydride groups per molecule andmore preferably contains 2 to 15 acid anhydride groups per molecule. Ifthe number of acid anhydride groups is less than 2, no sufficientcurability can be expected. If it is greater than 15, the cured productwill be too hard and brittle and lacking in adequate weather resistance.

As the above acid anhydride group-containing polymer (1c) is reactedwith the monohydric alcohol (1d), it is half- esterified so that apolymer containing both free and esterified carboxyl groups can beobtained. The end point of half-esterification reaction can be confirmedfrom substantial disappearance of the absorption of acid anhydridegroups at about 1785 cm⁻² on the infrared absorption spectrum.

The monohydric alcohol (1d) mentioned above is a low molecular weightcompound containing 1 to 12 carbon atoms and preferably a compound of 1to 8 carbon atoms, Where the carbon number is 1 to 12, the low molecularweight monohydric alcohol (1d) is vaporized on heating to favor theregeneration of the acid anhydride group.

The monohydric alcohol (1d) that can be used includes a variety ofalcohols of low molecular weight such as methanol, ethanol, propanol,butanol, methylcellosolve (trademark), ethylcellosolve (trademark),dimethylaminoethanol, diethylaminoethanol, acetol, allyl alcohol,propargyl alcohol, furfuryl alcohol and so on. Among them, acetol, allylalcohol, propargyl alcohol, methanol and furfuryl alcohol are preferred.

The ratio of said acid anhydride group-containing polymer (1c) andmonohydric alcohol (1d) for use in the above-mentionedhalf-esterification reaction is 1/10 to 1/1 in terms of the ratio of thenumber of mols of acid anhydride group in (1c) to the number of mols ofhydroxyl group in (1d). If the ratio is less than 1/10, the excessmonohydric alcohol tends to cause popping at the curing steps On theother hand, if the ratio exceeds 1/1, the unreacted acid anhydridegroups detract from the storage stability. The more preferred ratio is1/8 to 1/1.1.

The above half-esterification reaction can be carried out in theconventional manner at a temperature from room temperature to 120° C.

The polymer (1e) containing free and esterified carboxyl groups andhaving an acid value of 50 to 300 (mgKOH/g) as obtained by the abovereaction is used as a first component of the curable resin compositionof the present invention. If the acid value is less than 50, curabilitywill be poor. If 300 is exceeded, excessive hardness and decreases inweather resistance will be encountered. Neither of such polymers can beused for the purposes of the present invention.

The second component of the curable resin composition of this inventionis a hydroxyl group- and epoxy group-containing polymer (2d). The epoxyequivalent of the polymer (2d) is 200 to 1000 and the hydroxylequivalent thereof is 250 to 1500. If the epoxy equivalent is less than200, excessive hardening results in a brittle film. On the other hand,if 1000 is exceeded, the curability of the curable resin compositionwill become insufficient. Moreover, if the hydroxyl equivalent is lessthan 250, the water resistance of the cured coat will be insufficient.On the other hand, if 1500 is exceeded, only insufficient curability canbe obtained. The epoxy equivalent is preferably 250 to 800 and, forstill better results, 300 to 700. The hydroxyl equivalent is preferably300 to 1200 and, for still better results, 400 to 1000.

The above polymer (2d) containing hydroxyl and epoxy groups can beobtained by copolymerizing 5 to 60 weight %, preferably 15 to 40 weight%, of a hydroxyalkyl (meth) acrylate of general formula (I) with 10 to60 weight %, preferably 15 to 50 weight %, of an epoxy group-containingethylenically unsaturated monomer (2b), and where necessary, furtherwith 0 to 85 weight %, preferably 10 to 70 weight %, of one or moreother ethylenically unsaturated monomers (2c).

if the proportion of said hydroxyalkyl (meth)acrylate (2a) is less than5 weight %, no sufficient curability can be obtained. On the other hand,if 60 weight % is exceeded, compatibility is sacrificed so that thereaction cannot proceed to a sufficient extent. Moreover, if theproportion of said epoxy group-containing ethylenically unsaturatedmonomer (2b) is less than 10 weight %, curability will be insufficient.If 60 weight % is exceeded, excessive hardening and poor weatherresistance are encountered.

The carbon number of the hydroxyalkyl moiety of said hydroxyalkyl(meth)acrylate monomer (2a) is 2 to 20 and preferably 2 to 10. If thecarbon number is too large, the inter-crosslink molecular weight will beundesirably too large.

The hydroxyalkyl (meth)acrylate monomer (2a) that can be used includesbut is not limited to 2-hydroxy ethyl (meth)acrylate, hydroxypropyl(meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl(meth)acrylate, etc. and reaction products of these monomers withE-caprolactone. These compounds are available from commercial sources,and "Placcel FM1" and "Placcel FA1" (both manufactured by DaicelChemical Industries) can be mentioned. Moreover, such compounds can beprepared by esterifying (meth)acrylic acid with a large excess of a diolcompound.

The epoxy group-containing ethylenically unsaturated monomer (2b)mentioned above includes glycidyl (meth)acrylate, 2-methylglycidyl(meth)acrylate, 3,4-epoxycyclohexanylmethyl (meth)acrylate and so on.

The copolymerizable ethylenically unsaturated monomer (2c) mentionedabove includes, among others, these compounds mentioned specifically asexamples of said other ethylenically unsaturated monomer (1b)copolymerizable with acid anhydride group-containing ethylenicallyunsaturated monomer (1a).

The copolymerization reaction involving said hydroxyalkyl (meth)acrylatemonomer (2a), epoxy group-containing ethylenically unsaturated monomer(2b) and copolymerizable ethylenically unsaturated monomer (2c) can becarried out in the known manner, for example by the radicalpolymerization method in solution, at atmospheric pressure or atelevated pressure and a polymerization temperature of 100° to 200° C.for a polymerization time of 3 to 8 hours. As the polymerizationinitiator, a conventional initiator of the azo type or of the peroxidetype can be success fully employed. The above polymerization initiatoris used preferably in a proportion of 0.5 to 15 weight % based on thetotal monomer in the reaction system. Additives such as a chain transferagent can also be added to said monomer composition.

The number average molecular weight of the hydroxyl group- and epoxygroup-containing polymer (2d) as obtained by the above copolymerizationreaction is preferably 1500 to 8000 and, for still better results, 1800to 4000. If the number average molecular weight exceeds 8000, thepolymer viscosity becomes increased to interfere with preparation of ahigh-solid coating composition. On the other hand, if the molecularweight is less than 1500, the curability of the curable resincomposition will be insufficient.

The third component of the curable resin composition of the presentinvention is an alkoxyl group-containing silicone polymer having analkoxyl equivalent of 50 to 1500 (3a). This polymer is represented bygeneral formula (II).

The above mentioned silicone polymer (3a) is not particularly limited inkind only if it contains alkoxyl group(s) and includes those whichcontain epoxy group(s) along with alkoxyl group(s).

The alkoxyl group-containing silicone polymer mentioned above includes"KC-89S" manufactured by Shin-Etsu Chemical Industries, among others.The silicone polymer containing epoxy and alkoxyl groups includes "MKCSilicate MSEP2" series manufactured by Mitsubishi Kasei Corporation and"NUC Silicone" series manufactured by Nippon Unicar Co., among others.

The technology of producing a silicone polymer containing alkoxyl groupsis described in Synopsis of 1990 Symposium for the Chemistry of Organosilicon Materials, pp. 29 to 30.

When the above mentioned silicone polymer (3a) contains epoxy groups,the epoxy groups exist in intermediate or terminal positions of theacyclic or cyclic hydrocarbon chains. In silicone polymer (3a), theepoxy group-containing acyclic or cyclic hydrocarbon designated by Ymay, for example, be represented by any of the following formulas.##STR3##

In the above formulas, R¹¹, R¹² and R¹³ each represents a hydrocarbon of0 to 4 carbon atoms.

The alkoxyl equivalent of the silicone polymer (3a) according to thepresent invention is 50 to 1500. If the alkoxyl equivalent is less than50, the storage stability of the coating is sacrificed. If it exceeds1500, poor curability will result. The preferred range of alkoxylequivalent is 60 to 800 and the more desirable range is 80 to 500.

In this specification, "epoxy equivalent" means the number of grams of acompound containing one gram equivalent of epoxy group, "alkoxylequivalent" means the number of grams of a compound containing one gramequivalent of alkoxyl group, and "hydroxyl equivalent" means the numberof grams of a compound containing one gram equivalent of hydroxyl group.

In the present invention, an epoxy group-containing silicone polymer, ahydroxyl group- and carboxyl group-containing silicone polymer, etc. canalso be admixed along with said alkoxyl group-containing siliconepolymer (3a).

As the epoxy group-containing silicone polymer mentioned above, theremay be mentioned, among others, "NUC-Silicone" series manufactured byNippon Unicar.

As the hydroxyl group- and carboxyl group-containing silicone polymermentioned above, there may be mentioned, among others, "KR-2001"manufactured by Shin-Etsu Silicone Co. and "NUC-Silicone" seriesmanufactured by Nippon Unicar. The fourth component of the curable resincomposition of the present invention is a quaternary ammonium saltcatalyst (4a). In the present invention, the above mentioned quaternaryammonium salt catalyst (4a) is used in an amount of 0.1 to 5.0 weight %based on the resin solids. When it is used in an amount smaller than 0.1weight % poor curability will result. At levels above 5.0 weight %, thestorage stability of the coating is sacrificed. An addition level of 0.2to 3.0 weight % is more preferred, 0.5 to 1.5 weight % is still morepreferred.

As the above mentioned quaternary ammonium salt catalyst (4a), there maybe mentioned, among others, those which are used in esterificationreaction between acid and epoxy, such as benzyltriethylammoniumchloride, benzyltriethylammonium bromide, tetrabutylammonium chloride,tetrabutylammonium bromide, tetrabutylammonium salicylate,tetrabutylammonium glycolate, tetrabutylammonium p-toluenesulfonate,among others. These catalysts can be used in combination.

The fifth component of the curable resin composition of the presentinvention is a monoalkyltin compound (5a). In the present invention, theabove mentioned monoalkyltin compound (5a) is used in an amount of 0.1to 5.0 weight % based on the resin solids.

When it is used in an amount smaller than 0.1 weight %, the storagestability of the coating is sacrificed. At levels above 5.0 weight %,the poor curability will result. An addition level of 0.2 to 3.0 weight% is more preferred, 0.5 to 2.0 weight % is still more preferred.

The monoalkyltin compound (5a) mentioned above are not limited tospecific species but include monomethyltin tri(methylmalate),monomethyltin tri(ethylmalate), monomethyltin tri(butylmalate),monobutyltin tri(methylmalate), monobutyltin tri(ethylmalate),monobutyltin tri(butylmalate), among others.

Along with monoalkyltin compound (5a) mentioned above, in the presentinvention, a dialkyltin compound can be used jointly. When an acid-epoxycuring system is used, a dialkyltin compound is preferably used incombination. As examples for the dialkyltin compound, there may bementioned dibutyltin bis(methylmalate), dibutyltin bis(ethylmalate),dibutyltin bis(butylmalate), among others.

A technology for using the monoalkyltin compound for the purpose ofimproving the storage stability of the curing composition is disclosedin Japanese Kokai Publication Hei-5-302007. This technology uses vinylresin of which the main chain substantially comprises with vinylcopolymer and which containes hydrolyzable group-bindingsilicon-containing group (hydrolyzable silyl group), differs from thepresent invention as to the construction thereof.

Thus, the curable resin composition of this invention is produced bycompounding 5 to 80 weight % of said polymer (1e) containing free andesterified carboxyl groups, 1 to 80 weight % of a hydroxyl group- andepoxy group-containing polymer (2d), 1 to 50 weight % of an alkoxylgroup-containing silicone polymer (3a), 0.1 to 5.0 weight % of aquaternary ammonium salt catalyst (4a), and 0.1 to 5.0 weight % of amonoalkyltin compound (5a) as essential components. The weight % valuesgiven above are percentages based on the total solid matter of compounds(1e), (2d), (3a), (4a) and (5a). If the proportions of polymers (1e) and(2d) deviate from the above formulation ranges, curability issacrificed. If the proportion of silicone polymer (3a) is smaller thanthe above formulation range, the concentration of solids cannot beincreased. If (3a) is used too much, the composition becomes soft andsuffers from insufficient cure.

The above compounding ratio is specifically determined in such a mannerthat the molar ratio of the carboxyl group contained in said polymer(1e) to the epoxy group contained in said polymer (2d), namely the(carboxyl group)/(epoxy group) ratio, will be 1/1.6 to 1/0.6. In orderthat the molar ratio may fall within the above range, the proportions ofsaid three components of the five components of the present inventionare respectively selected within the range of (1e) 5 to 80 weight %, therange of (2d) I to 80 weight %, and the range of (3a) 1 to 50 weight %.The preferred ranges are (1e) 20 to 70 weight %, (2d) 10 to 70 weight %,and (3a) 5 to 30 weight %. The more desirable ranges are (1e) 30 to 60weight %, (2d) 15 to 60 weight %, and (3a) 8 to 25 weight %. If theabove ratio is smaller than 1/1.6, the coating film undergoes yellowing.On the other hand, if the ratio of 1/0.6 is exceeded, the curability ofthe product resin composition is sacrificed. The above molar ratio ismore preferably 1/1.3 to 1/0.8. It should be understood that when said(3a) contains epoxy group(s), said number of moles of epoxy group is thesum of numbers of moles of epoxy group contained in said (2d) andnumbers of moles of epoxy group contained in said (3a). It should alsobe understood that when a silicone polymer containing hydroxyl andcarboxyl groups is used in addition to said (3a), said number of molesof carboxyl group is the sum of numbers of moles of carboxyl groupcontained in said (1e) and said silicone polymer containing hydroxyl andcarboxyl groups.

The nonvolatile matter (SVS) in the curable resin composition of thisinvention is preferably not less than 40% in terms of volume and morepreferably not less than 45% on the same basis. If the amount ofnonvolatile matter is less than the above level, the composition is notsuitable for use in the areas where regulations for solvent control arein force.

The mechanism of cure of the curable resin composition of this inventionis now explained. First, on heating, the carboxyl group and carboxylicester group in (1e) react to give an acid anhydride group within (1e),with liberation of free monohydric alcohol. The monohydric alcohol soproduced is vaporized and removed from the reaction system. The acidanhydride group generated in (1e) reacts with the hydroxyl group of (2d)to form a crosslink and a free carboxyl group is regenerated. Thiscarboxyl group and the carboxyl group initially present in (1e) reactwith the epoxy groups in (2d) or, where (3a) contains an epoxy group,with the epoxy groups of (2d) and (3a) to form crosslinks.

On the other hand, when (3a) contains alkoxyl groups, the alkoxyl groupof (3a) reacts with the hydroxyl group of (2d) to form a crosslink. Theliberated monohydric alcohol is vaporized and removed from the reactionsystem. The alkoxyl group is hydro lyzed by the water present in thereaction system to give a silanol group and a monohydric alcohol. Themonohydric alcohol thus produced is evaporated and removed from thereaction system. The silanol group formed in (3a) undergoes dehydrativecondensation with the hydroxyl group of (2d) and between silanol groupsto form crosslinks. The byproduct water is vaporized and removed fromthe system. The silanol group reacts with the alkoxyl group to form acrosslink with elimination of alcohol. The alcohol thus liberated isvaporized and removed from the system. In this manner, the curable resincomposition cures progressively as the result of interaction of (1e),(2d) and (3a).

It will be apparent from the above reactions that where (3a) containsalkoxyl groups, the alkoxyl group invariably exists in the form of analkoxysilyl group.

For enhanced crosslinking density and improved water resistance of thecurable resin composition of the present invention, an aminoplast curingagent, a blocked isocyanate, etc. can also be employed. Melamine resinand others can be mentioned as examples and one or more of them can beemployed.

There is no particular limitation on the method for production of thecurable resin composition of the present invention.

The coating composition of the present invention can be provided byformulating the curable resin composition of the present invention inthe conventional manner. As the solvent for use in the production of thecoating composition of the present invention, organic solvents that areconventionally used in coatings or a mixture of such solvents can beemployed. Among such solvents may be mentioned aromatic hydrocarbonsolvents such as toluene and xylene, aliphatic hydrocarbon solvents suchas n-hexane and heptane, petroleum cracking fractions composedpredominantly of aliphatic hydrocarbons and containing aromatichydrocarbons, esters such as butyl acetate, ethylene glycol diacetate,2-ethoxyethyl acetate, etc., ketones such as methyl isobutyl ketone, andalcohols such as butyl alcohol.

For improved weather resistance of the coat formed from said coatingcomposition, an ultraviolet absorber, e.g. benzophenone derivatives,benzotriazole derivatives, etc., a hindered amine light stabilizer, aphenolic antioxidant, etc. can be added. Aside from the above additives,a rheology modifier (an agent for sag control) such as a particulatecrosslinked resin, and a surface modifier for modulating the appearanceof the coat can also be added.

For adjusting the viscosity of said coating composition, among otherpurposes, an alcoholic solvent such as methanol, ethanol, propanol,butanol, etc., a hydrocarbon solvent, an ester solvent or the like canbe used as the diluent.

For an increased storage stability of said coating composition, ahydrolyzable ester solvent such as trimethyl orthoformate, trimethylorthoacetate, triethyl orthoacetate, etc. can also be added. Thepreferred level of addition of this solvent is 1 to 10 weight % relativeto the paint.

The coating composition of the present invention can be applied by spraycoating, brush coating, dip coating, roll coating, flow coating, rotaryatomizing coating or other method.

For use of the coating composition of the present invention as a clearpaint, the composition may be applied by the per se conventional methodbut, if desired, after application of a base coat to a substrate, it maybe coated on the base coat in a wet-on-wet manner. The coating for thebase coat may be water-based or solvent-based but where a water-basedcoating is used, the base coat is preferably heated at 60° C. to 100° C.for 2 to 10 minutes prior to application of the clear paint so that amore satisfactory finished film may be obtained.

The coating composition of the present invention can be applied toessentially all kinds of substrates, such as wood, metal, glass, cloth,plastics, foams, etc. or surfaces treated with a variety of primers. Thecoating composition of the present invention can be applied withparticular advantage to plastic and metallic surfaces. Generally theoptimum film thickness varies with different uses but is preferably 20to 100 μm in many instances.

After application, the coat is cured. To attain a cured coating film ofhigh crosslink density, curing is performed at 100° to 180° C. andpreferably at 120° to 160° C. The necessary cure time depends on curingtemperature but may generally be 10 to 30 minutes at 120° to 160° C.

The curable resin composition of the present invention can be usedadvantageously as a clear coating composition. As the base coating foruse in this application, a color pigment-containing water-based coatingor a color pigment-containing organic solvent type coating is preferred.The preferred coating method is the two-coat one-bake method whichcomprises coating the curable resin composition of the present inventionon a based coat which has not been cured as yet and baking the two coatsat a time.

However, when a water-based coating is used, the base coat is preferablyheated at 60° to 100° C. for 2 to 10 minutes prior to application of theclear coating in order to achieve an improved finished appearance. Asthe base coating, the coatings disclosed in U.S. Pat. No. 5,151,125 andU.S. Pat. No. 5,183,504 can be utilized. Particularly the water-basedcoating composition described in Example 1 of U.S. Pat. No. 5,183,504 ismost suitable in terms of finished appearance and performancecharacteristics.

When the curable resin composition of the present invention is used as aclear coating composition, a still more satisfactory coat can beobtained by a method which comprises coating a clear coating compositioncontaining the curable resin composition of the present invention on thesurface of a base coat and further coating the clear coating compositioncontaining the curable resin composition of the present invention insuperimposition as a finish coat.

Coating compositions containing the curable resin composition of thepresent invention as a binder component can be coated on variousarticles. The articles that can be coated are virtually not limited onlyif the curable resin composition can be heat-cured thereon. Thus, forexample, automotive bodies and car parts such as wheels and bumpers,household electrical appliances such as air-conditioner outdoorinstallations, and building materials such as exterior sidings.

EXAMPLES

The following examples are further illustrative of the present inventionbut by no means limitative of the scope of the present invention.

Production Example 1

A polymer containing carboxyl and carboxylic anhydride groups

A 3L reactor equipped with a thermometer, stirrer, condenser, nitrogeninlet pipe and drip funnel was charged with 700 parts by weight ofxylene and 350 parts by weight of Solvesso 100 and the temperature wasincreased to 130° C. Using the drip funnel, a solution composed of 300parts by weight of styrene monomer, 109 parts by weight of 2-ethylhexylmethacrylate, 325 parts by weight of isobutyl acrylate, 25.7 parts byweight of acrylic acid, 240 parts by weight of maleic anhydride, 300parts by weight of propyleneglycol monomethyl ether acetate, 150 partsby weight of t-butylperoxy-2-ethylhexanoate and 150 parts by weight ofxylene was fed dropwise to the reactor over a period of 3 hours. Aftercompletion of dropwise addition, the mixture was maintained at 130° C.for 30 minutes, at the end of which time a solution composed of 20 partsby weight of t-butylperoxy-2-ethylhexanoate and 20 parts by weight ofxylene was added dropwise over 30 minutes. After completion of dropwiseaddition, the reaction was further continued at 130° C. for one hour andthe solvent was then distilled off 1100 parts by weight of the solventto provide a carboxyl group- and carboxylic anhydride group-containingpolymer solution (a-1) with a nonvolatile content of 70% and a numberaverage molecular weight of 2000.

Production Example 2

A polymer containing free and esterified carboxyl groups

To 1590 parts by weight of the polymer solution (a-1) obtained inProduction Example 1 were added 2 parts by weight of triethylamine and125 parts by weight of methanol and the reaction was conducted at 60° C.for 8 hours to provide a polymer solution (A-1) containing free andesterified carboxyl groups. The infrared absorption spectrum of thispolymer solution (A-1) was determined to confirm disappearance of acidanhydride absorption (1785 cm⁻²). The acid value of the solid matter ofthis polymer solution (A-1) was 158 (mgKOH/g).

Production Example 3

A polymer containing hydroxyl and epoxy groups

A 3L reactor equipped with a thermometer, stirrer, condenser, nitrogengas inlet pipe and drip funnel was charged with 700 parts by weight ofxylene and 525 parts by weight of propyleneglycol monomethyl etheracetate and the temperature was increased to 130° C. Through the dripfunnel, a solution containing 200 parts by weight ofpara-t-butylstyrene, 354 parts by weight of glycidyl methacrylate, 139parts by weight of 2-hydroxyethyl methacrylate, 176 parts by weight ofcyclohexyl acrylate, 131 parts by weight of isobornyl methacrylate, 120parts by weight of t-butylperoxy-2-ethylhexanoate, and 200 parts byweight of xylene was dripped into the reactor over 3 hours. Aftercompletion of dropwise addition, the reaction mixture was maintained at130° C. for 30 minutes. Then, a solution composed of 10 parts by weightof t-butylperoxy-2-ethylhexanoate and 50 parts by weight of xylene wasadded dropwise over 30 minutes. After completion of dropwise addition,the reaction was further continued at 130° C. for one hour, at the endof which time 1200 parts by weight of the solvent was distilled off toprovide a polymer solution (B-1) containing both hydroxyl and epoxygroups and having a nonvolatile content of 77%, a number averagemolecular weight of 1800, an epoxy equivalent of 402 and a hydroxylequivalent of 935.

The silicone polymer containing alkoxyl group(s)

The silicone polymer of general formula (II) wherein R¹, R³ and R⁶ eachrepresents methyl and R² and R⁴ each represents that ofmethoxy/butoxy=1/1, R⁵ represents that of methoxy/γ-glycidoxypropyl=1/1,q=5, m=4, n=2 and having an epoxy equivalent of 625 and an alkoxylequivalent of 83 (manufactured by Mitsubishi Kasei Corporation, MKCSilicate MSEP-HB2) was used as an epoxy group- and alkoxylgroup-containing polymer solution (C-1).

A silicone polymer of general formula (II) wherein R¹ and R¹ eachrepresents methyl, R², R⁴ and R⁵ each represents methoxy, q=7, m=2, n=0and having an alkoxyl equivalent of 81 (manufactured by Shin-EtsuChemical Co., KC-89S) was used as an alkoxyl group-containing polymersolution (C-2).

A silicone polymer of general formula (II) wherein R¹ represents methyl,R² represents that of γ-glycidoxypropyl/(trimethoxysilyl)ethyl=2/1, R³,R⁴ and R⁵ each represents methyl, q=6, m=2, n=0, and having an epoxyequivalent of 318 and an alkoxyl equivalent of 213 (manufactured byNippon Unicar Co., F-244-09) was used as an epoxy group- and alkoxylgroup-containing polymer solution (C-3).

Quaternary ammonium salt catalyst

Tetrabutylammoninm glycolate was used as (D-1).

Tetrabutylammoninm salicylate was used as (D-2).

Tetrabutylammoninm paratoluensulfonate was used as (D-3).

Tetrabutylammoninm bromide was used as (D-4).

Tetrabutylphosphonium bromide was used as (D-5).

Dialkyltin compound

Dibutyltin diacetate was used as (E-1).

Dibutyltin bis(butyllaurate ) was used as (E-2).

Dibutyltin bis(butylmalate) was used as (E-3).

Monoalkyltin compound

Monobutyltin triacetate was used as (E-4).

Monobutyltin tris(monobenzilmalate) was used as (E-5).

Monobutyltin trioctylate was used as (B-6).

Monobutyltin trichloride was used as (E-7).

Monobutyltinthioglycollic acid octyl ester was used as (E-8).

Monobutyltin β-mercaptopropionic acid octyl ester was used as (E-9).

Melamine resin

Cymel 327 (manufactured by Mitsui-Cytec Co.) was used as (F-1).

Stabilizer

Triethyl orthoformate was used as (G-1).

Surface conditioner

Modaflow (manufactured by Monsanto) was used as (H-1).

Ultraviolet absorber

Tinuvin 900 (manufactured by Ciba-Geigy) was used as (I-1).

Antioxidant

Tinuvin 123 (manufactured by Ciba-Geigy) was used as (J-1).

Production Example 4

Preparation of a coated plate

A 0.8 mm-thick dull steel plate treated with zinc phosphate waselectrocoated with a cationic electrodeposition paint (Power Top pu-50,Nippon Paint Co.) in a dry thickness of about 25 μm. This electrocoatingfilm was further air spray-coated with an intermediate coating (Orga P-2intermediate coat, manufactured by Nippon Paint Co.) in a dry thicknessof about 40 μm , followed by 30-minute baking at 140° C.

Then, this coated plate was air spray-coated with an acryl-melaminesolvent type base paint (manufactured by Nippon Paint Co.) in a drythickness of about 16 μm followed by about 7 minutes' setting. Where awater-based-base coating (manufactured by Nippon Paint Co.) was used,air spray-coating was followed by about 1 minute of setting and 5minutes' preheating at 80 C.

The solvent type base coating was prepared by compounding 50 parts byweight of an acrylic resin (80% solids, acid value=30, OH value=100,number average molecular weight 1800), 40 parts by weight of Cymel 202(Mitsui Cytec Co.) and 10 parts by weight of Cymel 327 (Mitsui CytecCo.) for melamine resin, 10 parts by weight of Alpaste 60-600(ToyoAluminum Co.) for pigment, and 7 parts by weight of isopropyl alcohol.

The water-based base coating was prepared by formulating 56 parts byweight of aqueous acrylic resin (50% solids, acid value=58, OH value=70,number average molecular weight=12000), 15 parts of Cymel 303 (MitsuiCytec Co.), 21.5 parts by weight of urethane emulsion (33% solids, acidvalue=16.2), 7.5 parts by weight of Alpaste 7160N (Toyo Aluminum Co.)for pigment, and 1 part by weight of isostearyl phosphate forstabilizer.

Coating with the coating composition of the invention

Coating compositions of the solid compositions shown in Tables 1 and 2were respectively adjusted to a Ford cup No. 4 viscosity of 30 secondsand using an electrostatic coating machine, Auto Rea (Randsburg-Gema),each was coated at a spray pressure of 5 kg/cm² in a dry film thicknessof about 40μm and after about 7 minutes of setting, baked at 140° C. for25 minutes.

Evaluation of coating film characteristics

1. SVS (nonvolatile matter)

After the viscosities of the coatings were uniformly adjusted to a Fordcup No. 4 viscosity of 30 seconds/20° C. 0.5 g was accurately taken fromeach coating, diluted with 3 cc of toluene, baked at 110 C. for onehour, and the nonvolatile matter (weight) was determined and convertedto volume. The results are shown in Tables 1 and 2.

2. Pencil hardness

Determined according to JIS K 5400, 8.4.2.

3. Water resistance

Each testpiece was immersed in tap water at 40° C. and allowed to standfor 10 days. Thereafter, the coating film of the testpiece was visuallyinspected. Evaluation was made according to the following criteria. Theresults are shown

in Tables 1 and 2.

◯: No abnormality

Δ: Slight film abnormality

×: Overt film abnormality

4. Mar resistance

A 2×2 cm flannel cloth coated with 1 g of 50% aqueous dispersion ofcleanser (New Homing Cleanser, Kao Corporation) was mounted on aGakushin-type color friction fastness tester (manufactured by DaieiKagaku Seiki). Under a load of 500 g, the sliding head was reciprocatedfor 20 cycles and the 20°. gloss of the test area was determined tocalculate the gloss retention. The results are shown in Tables 1 and 2.

⊚: gloss retention ≧85%

◯: gloss retention ≧70% to <85%

Δ: gloss retention ≧40% to <70%

×: gloss retention <40%

5. Acid resistance

The specimen was contacted with 0.5 cc of 1wt. % aqueous solution ofsulfuric acid at 75° C. for 30minutes and the surface of the coat wasvisually inspected and evaluated according to the following criteria.The results are shown in Tables 1 and 2.

⊚: No abnormality

◯: Small traces

Δ: Large traces

×: Film abnormalities found

6. Storage stability

After the viscosities of the coatings were uniformly adjusted to a Fordcup No. 4 viscosity of 30 seconds/20° C. the coatings were stored for 10days at 40° C. After that, the viscosity changes (seconds) were measuredby Ford cup No. 4 method at 20° C. The results are shown in Table 1 andTable 2.

                                      TABLE 1                                     __________________________________________________________________________              Examples                                                                      1   2   3   4   5   6   7   8   9   10  11  12                      __________________________________________________________________________    Polymer                                                                       A-1       43.7                                                                              43.7                                                                              43.7                                                                              43.7                                                                              43.7                                                                              43.7                                                                              43.7                                                                              43.7                                                                              43.7                                                                              43.7                                                                              43.7                                                                              43.7                    B-1       36.3                                                                              36.3                                                                              36.3                                                                              36.3                                                                              36.3                                                                              36.3                                                                              36.3                                                                              36.3                                                                              36.3                                                                              36.3                                                                              36.3                                                                              36.3                    C-1       20.0                                                                              20.0                                                                              20.0                                                                              20.0                                                                              20.0                                                                              20.0                                                                              20.0                                                                              20.0                                                                              20.0                                                                              20.0                                                                              20.0                                                                              20.0                    C-2       --  --  --  --  --  --  --  --  --  --  --  --                      C-3       --  --  --  --  --  --  --  --  --  --  --  --                      Quaternary ammonium                                                           salt catalyst                                                                 D-1       1.0 --  --  --  --  1.0 1.0 1.0 1.0 1.0 --  --                      D-2       --  1.0 --  --  --  --  --  --  --  --  --  --                      D-3       --  --  1.0 --  --  --  --  --  --  --  --  --                      D-4       --  --  --  1.0 --  --  --  --  --  --  1.0 1.0                     D-5       --  --  --  --  1.0 --  --  --  --  --  --  --                      Alkyls tin compound                                                           E-1       --  --  --  --  --  --  --  --  --  --  --  --                      E-2       --  --  --  --  --  --  --  --  --  --  --  --                      E-3       --  --  --  --  --  --  --  --  --  --  --  --                      E-4       --  --  --  --  --  1.0 --  --  --  --  --  --                      E-5       --  --  --  --  --  --  1.0 --  --  --  --  --                      E-6       1.0 1.0 1.0 1.0 1.0 --  --  --  --  --  0.5 2.0                     E-7       --  --  --  --  --  --  --  1.0 --  --  --  --                      E-8       --  --  --  --  --  --  --  --  1.0 --  --  --                      E-9       --  --  --  --  --  --  --  --  --  1.0 --  --                      F-1       --  --  --  --  --  --  --  --  --  --  --  --                      G-1       2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2 0 2.0 2.0                     H-1       1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5                     I-1       2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0                     J-1       1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0                     Base paint                                                                              solvent                                                                           solvent                                                                           solvent                                                                           solvent                                                                           solvent                                                                           solvent                                                                           solvent                                                                           solvent                                                                           solvent                                                                           solvent                                                                           solvent                                                                           solvent                           type                                                                              type                                                                              type                                                                              type                                                                              type                                                                              type                                                                              type                                                                              type                                                                              type                                                                              type                                                                              type                                                                              type                    S V S     51.3                                                                              51.4                                                                              52.2                                                                              52.4                                                                              52.3                                                                              51.3                                                                              51.3                                                                              51.2                                                                              51.4                                                                              51.3                                                                              51.4                                                                              51.6                    Pencil scratch test                                                                     H   H   F   H   H   H   H   H   H   H   F   H                       Water resistance                                                                        ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯           Mar resistance                                                                          ⊚                                                                  ⊚                                                                  ◯                                                                     ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                                                                  ◯                                                                     ◯                                                                     ⊚        Acid resistance                                                                         ⊚                                                                  ⊚                                                                  ◯                                                                     ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                                                                  ◯                                                                     ◯                                                                     ⊚        Storage stability                                                                       14.8                                                                              16.6                                                                              11.6                                                                              20.4                                                                              20.2                                                                              16.4                                                                              15.4                                                                              14.4                                                                              15.8                                                                              16.2                                                                              24.8                                                                              16.0                    __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________               Examples                 Comparative Examples                                 13  14  15  16  17  18   1   2   3   4   5   6                     __________________________________________________________________________    Polymer                                                                       A-1        43.7                                                                              43.7                                                                              37.6                                                                              49.5                                                                              43.7                                                                              39.3 43.7                                                                              43.7                                                                              43.7                                                                              43.7                                                                              43.7                                                                              Commercial            B-1        36.3                                                                              36.3                                                                              42.4                                                                              30.5                                                                              36.3                                                                              32.7 36.3                                                                              36.3                                                                              36.3                                                                              36.3                                                                              36.3                                                                              melamine-             C-1        20.0                                                                              20.0                                                                              --  --  20.0                                                                              18.0 20.0                                                                              20.0                                                                              20.0                                                                              20.0                                                                              20.0                                                                              containing            C-2        --  --  20.0                                                                              --  --  --   --  --  --  --  --  high-solid            C-3        --  --  --  20.0                                                                              --  --   --  --  --  --  --  coating               Quaternary ammonium                                     composition           salt catalyst                                                                 D-1        0.5 --  1.0 1.0 --  --   1.0 1.0 1.0 1.0 --                        D-2        --  1.5 --  --  --  --   --  --  --  --  --                        D-3        --  --  --  --  --  --   --  --  --  --  --                        D-4        --  --  --  --  1.0 1.0  --  --  --  --  --                        D-5        --  --  --  --  --  --   --  --  --  --  --                        Alkyls tin compound                                                           E-1        --  --  --  --  --  --   1.0 --  --  --  --                        E-2        --  --  --  --  --  --   --  1.0 --  --  --                        E-3        --  --  --  --  --  --   --  --  1.0 --  --                        E-4        --  --  --  --  --  --   --  --  --  --  --                        E-5        --  --  --  --  --  --   --  --  --  --  --                        E-6        1.0 1.0 1.0 1.0 1.0 --   --  --  --  --  1.0                       E-7        --  --  --  --  --  --   --  --  --  --  --                        E-8        --  --  --  --  --  --   --  --  --  --  --                        E-9        --  --  --  --  --  --   --  --  --  --  --                        F-1        --  --  --  --  --  10.0 --  --  1.0 1.0 1.0                       G-1        2.0 2.0 2.0 2.0 2.0 2.0  2.0 2.0 2.0 2.0 2.0                       H-1        1.5 1.5 1.5 1.5 1.5 1.5  1.5 1.5 1.5 1.5 1.5                       I-1        2.0 2.0 2.0 2.0 2.0 2.0  2.0 2.0 2.0 2.0 2.0                       J-1        1.0 1.0 1.0 1.0 1.0 1.0  1.0 1.0 1.0 1.0 1.0                       Base paint solvent                                                                           solvent                                                                           solvent                                                                           solvent                                                                           water-                                                                            solvent                                                                            solvent                                                                           solvent                                                                           solvent                                                                           solvent                                                                           solvent                                                                           solvent                          type                                                                              type                                                                              type                                                                              type                                                                              based                                                                             type type                                                                              type                                                                              type                                                                              type                                                                              type                                                                              type                  S V S      51.5                                                                              51.1                                                                              52.4                                                                              51.9                                                                              52.4                                                                              50.7 51.3                                                                              51.3                                                                              51.2                                                                              51.0                                                                              52.0                                                                              49.0                  Pencil scratch test                                                                      F   H   F   H   H   2H   F   F   F   HB  2B  F                     Water resistance                                                                         ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                      ◯                                                                     ◯                                                                     ◯                                                                     Δ                                                                           X   ◯         Mar resistance                                                                           ◯                                                                     ⊚                                                                  ◯                                                                     ⊚                                                                  ⊚                                                                  ⊚                                                                   ⊚                                                                  ⊚                                                                  ⊚                                                                  Δ                                                                           Δ                                                                           Δ               Acid resistance                                                                          ◯                                                                     ⊚                                                                  ◯                                                                     ⊚                                                                  ⊚                                                                  ◯                                                                      ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     Δ                                                                           X                     Storage stability                                                                        10.4                                                                              21.0                                                                              12.6                                                                              18.4                                                                              20.4                                                                              13.4 55.3                                                                              51.2                                                                              58.5                                                                              80.5                                                                              15.2                                                                              13.6                  __________________________________________________________________________

INDUSTRIAL APPLICABILITY

The curable resin composition of this invention provides for a coatingfilm with high acid resistances and mar resistance and imparts a highquality appearance and further, has a sufficient storage stability.

The coating composition obtainable with the curable resin composition ofthis invention can be provided with a high-solid feature and can beadvantageously used for automotive parts and exterior buildingmaterials, among other uses.

We claim:
 1. A curable resin composition comprising5 to 80 weight % of apolymer containing free and esterified carboxyl groups and having anacid value of 50 to 300 (mg KOH/g) (1e) as obtainable by reacting anacid anhydride group-containing polymer (1c), which is obtainable bycopolymerizing 10 to 40 weight % ol an acid anhydride group-containingethylenically unsaturated monomer (1a) with 90 to 60 weight % of acopolymerizable other ethylenically unsaturated monomer (1b), with amonohydric alcohol of 1 to 12 carbon atoms (1d) in the ratio (the numberof mols of acid aihydride group in acid anhydride-containing polymer(1c))/(the number of mols of hydroxyl group in monohydric alcohol (1d))of 1/10 to 1/1, 1 to 80 weight % of a hydroxyl group- and epoxygroup-containing polymer having an epoxy equivalent of 200 to 1000 and ahydroxyl equivalent of 250 to 1500 (2d) as obtainable by copolymerizing5 to 60 weight % of a hydroxylalkyl (meth) acrylate monomer (2a) of thegeneral formula (I): ##STR4## wherein R represents hydrogen or methyl; Arepresents a straight-chain or branched alkylene group of 2 to 8 carbonatoms; y represents a whole number of 3 to 7; z represents a wholenumber of 0 to 4; with 10 to 60 weight % of an epoxy group-containingethylenically unsaturated monomer (2b) and 0 to 85 weight % of anethylenically unsaturated monomer (2c) copolymerizable therewith, 1to 50weight % of an alkoxyl group-containing silicone polymer having analkoxyl equivalent of 50 to 1500 (3a) of the general formula (II):##STR5## wherein R¹, R², R³, R⁴, R⁵, and R⁶ are the same of differentand each represents alkyl of 1 to 10 carbon atoms, phenyl, phenethyl,alkoxyl of 1 to 5 carbon atoms, R'--Si(OR')₃, R⁷ --Si(OR')₂ CH₃, R⁷--Si(OR⁸)(CH₃)₂, or R⁷ --Y; R⁷ represents a straight-chain or branchedalkylene group which may have an ether bond and/or an ester bond; R⁸represents alkyl of I to 5 carbon atoms; Y represents an epoxygroup-containing acyclic or cyclic hydrogen group; q represents a wholenumber of 1 to 20, m represents a whole number of 0 to 4, n represents awhole number of 0 to 2; the q, m and n repetitions are a randomarrangement coupled with the unit structures which are separate fromeach other;
 0. 1 to 5.0 weight % of a quaternary ammonium salt catalyst(4a), and0.1 to 5.0 weight % of a monoalkyltin compound (5a).
 2. Thecurable resin composition according to claim 1 wherein saidcopolymerizable other ethylenically unsaturated monomer (1b) is acarboxyl group-containing monomer (1b²).
 3. The curable resincomposition according to claim 1 which contains a hydrolyzable estersolvent.
 4. A coating composition comprising as a binder component thecurable resin composition of claim
 1. 5. A method of producing a coatingfilm comprising the following steps: (A) a step of forming an undercoatlayer, and an intermediate coating layer where necessary, on asubstrate, (B) a step of coating a water-based or solvent-based coatingon the undercoat or intermediate coating layer formed in step (A), (C) astep of coating the coating composition of claim 4 in superimposition tosaid water-based or solvent-based coating prior to curing of saidwater-based or solvent-based coating or after curing of said water-basedor solvent based coating, and (D) a step of causing said water-based orsolvent-based coating formed in step (B) and said coating composition ofclaim 4 from step (C) to cure or only said coating composition of claim4 from step (C) to cure.
 6. A coated article characterized in that ithas a coating layer formed from the coating composition of claim
 4. 7.The curable resin composition according to claim 2 which contains ahydrolyzable ester solvent.
 8. A coating composition characterized inthat it contains the curable resin composition of claim 2 as a bindercomponent.
 9. A coating composition characterized in that it containsthe curable resin composition of claim 3 as a binder component.